The invention relates to a sleeve-shaped device to retain screws while these are turned into an object, such as a bone, by means of a screw-driver.
Devices of such a type have been generally known as shown in U.S. Pat. Nos. 3,498,351 and 4,763,548. For example, such devices make it easier for a surgeon to screw in bone screws or similar screws under poor handling and visual conditions. The expandable portion serves for receiving the screw, particularly the screw head and, thus, enables a screw to be received at a location remote from the object. Here, the shank of the screw-driver may already be within the catch or gripping sleeve and its blade or its corresponding engaging end may already have been brought into engagement with the screw. The safety sleeve is displaceable on the catch or gripping sleeve and serves for locking the expandable portion in order that the screw be caught in the catch sleeve during the turn-in operation. For this purpose, the safety sleeve is slidingly movable between two positions on the catch sleeve. It takes its blocking positioning when in the front position, and allows an expansion of the expandable portion, when in the rear position. This allows the device to receive a screw or to be removed from the screw which was turned in.
The safety sleeve usually is biased towards the blocking position by means of a spring. However, if such a device is inserted there is a risk of the safety sleeve being pushed back against the spring, e.g. by surrounding soft parts, while the device is being inserted into the location at which a screw is intended to be turned in, which no longer guarantees the securing function of the safety sleeve.
Therefore, it is the object of this invention to provide a sleeve-shaped device to retain screws while these are turned into an object by means of a screw-driver wherein the safety sleeve maintains it blocking position regardless of external forces engaging it.
According to the invention, the safety sleeve is locked on the catch sleeve, i.e. by means of at least one ball, for example mounted on the safety sleeve. The ball engages an annular groove in the catch sleeve and is impeded by an inner portion of the second handle portion from moving outwardly. If the second handle portion is moved relative to the safety sleeve or the catch sleeve relative motion initially does not take place between the sleeves, i.e. the safety sleeve thus cannot be moved into the releasing position from the blocking position. Not until the second handle portion reaches a relative position in which the ball may escape into a recess within the second handle portion which may occur while a first spring is compressed between the handle portion and a shoulder of the safety sleeve. The first spring may move the safety sleeve again with respect to the second handle portion towards a stop into a releasing position. The second handle portion initially has moved away from the safety sleeve during its motion while the first spring is compressed.
After the locking mechanism is released the safety sleeve is allowed to follow by sliding while the first spring is released so that the expandable portion now can receive or release a screw. The shank of the screw-driver which is passed through the catch sleeve is located by means of another locking ball which engages an annular groove of the shank. Also here, a portion of the second handle portion normally prevents the locking ball from moving out. If the two components are intended to be separated from each other the second handle portion is required to move a predetermined distance relative to the catch sleeve against the force of the further spring until the aforementioned locking ball enters a further recess of the second handle portion. The distance required to be passed through here is larger than the distance which is needed for a relative motion between the second handle portion and the safety sleeve in order that this locking ball can be moved into the releasing position.
It follows from the above explanation that the safety sleeve, when in the blocking position, is prevented from axially moving to the releasing position and, thus, cannot be displaced by forces applied from the outside. Such forces, for example, will occur if the assembly is passed through a tissue until the screw which has been received is screwed in the desired location, e.g. into a bone.
According to an aspect of the invention, the first spring preferably is weaker than the second spring. According to another aspect of the invention, the second handle portion has a sleeve portion and a handling portion which are in an operative communication with each other. For example, the sleeve portion may be screwed onto an axial collar of the handling portion.
According to a further aspect of the invention, the second inner shoulder of the second handle portion and the radial recess are defined by a ring which is disposed within the second handle portion. For example, the ring may be screwed into the sleeve-shaped portion of the second handle portion. The described recesses into which the locking balls may escape preferably are formed in a ring shape in the interior of the second handle portion.